Blood circulates through a blood vessel of a person or an animal and carries oxygen inhaled in the lungs to tissue cells and carries carbon dioxide from the tissue to the lungs to discharge it from the body. Further, the blood carries a nutriment absorbed in an alimentary canal to organs or tissue cells and carries degradation products from tissues, that is, materials unnecessary for a live body to a kidney to be discharged from the body, and carries hormones secreted from an endocrine gland to functional organs and tissues. Further, the blood performs various actions, such as equally distributing body heat to constantly maintain body temperature, destructing or detoxifying bacteria or foreign objects infiltrated in a live body, or the like.
The blood, which is a main index for determining various diseases or a health state, is an index to perform diagnoses and prognosis management for diseases associated with protein by measuring presence or absence of specific protein or an amount thereof using a blood analyzer. Recently, a biochip capable of easily and rapidly diagnosing and analyzing specific diseases by injecting a small amount of blood into a disposable chip in a strip type has been developed. The biochip may rapidly and inexpensively perform various blood tests and analyses requiring a long period of time without using professionals or special test equipment.
The blood consists of blood cells including leukocyte, erythrocyte, platelet, or the like, and plasma including water, protein, fat, sugar, and other minerals. The protein to be detected is mainly present in the plasma. In order to obtain high sensitive, reproducible results, the blood cells are removed from the blood by using the biochip and only the plasma component is used to measure and detect the protein. Therefore, a plasma filter element for effectively filtering only the plasma component in the blood is required as a kind of pre-processor of the biochip and is an important component for accuracy and precision of the biochip.
There are various methods for filtering plasma from whole blood in the related art. For example, there are a method for filtering blood cells and plasma using centrifugal force, a method for extracting plasma by filtering the blood cells from blood using a fine structure disposed in a channel, having a smaller size than the blood cells, a method for extracting only a plasma component from blood by installing a diaphragm having a low height so as to prevent blood cells from passing therethrough, a method for filtering blood cells by disposing paper, a glass fiber, a porous medium, a membrane, or the like, at a side or front in which blood flows, a method for extracting only plasma by forming layers of blood cells and plasma using a precipitation effect of blood cells due to gravity, and a method for deflecting a flow of blood cells by applying electrical signals to blood.
As described above, as requirements of the filter for separating plasma on the biochip, use of a small amount of sample blood, high blood cell removal efficiency, simple operation, non-dilution, speed, reproducibility, inexpensive disposable use, and compatibility, or the like, are needed.
However, the filter for filtering plasma according to the related art satisfies only some of these requirements or has only the characteristic functions and therefore, has a limitation in structural and functional aspects which do satisfy all the requirements.